# At what angle does a single atom “reflect” a single photon?

Does this question make sense in the quantum world?

Imagining a single photon (wave packet?) interacting with a single atom (its electrons etc) how do we currently describe/define the emitted photon in terms of its direction in relation to the incoming photon?

Now "scaling up" to a surface of atoms actually reflecting "light" according to the simple reflection rules like angle-in equals angle-out how do we manage to explain this effect in terms of the quantum world? How comes the probabilities work out for the out-going angle depending on the incoming-angle?

• Just remember that energy, momentum and angular momentum have to be conserved and you will get a spatial probability distribution. Of course, you have to take into account the recoil velocity of the atom as well. – Antillar Maximus Mar 9 '12 at 0:47
• I can only add this links Emergence of a measurement basis in atom-photon scattering, Y. Glickman, S. Kotler, N. Akerman and R. Ozeri, Science, 339, 1187 (2013) sciencemag.org/content/339/6124/1187 Reversal of photon scattering errors in atomic qubits, N. Akerman, S. Kotler, Y. Glickman and R. Ozeri, Phys. Rev. Lett. 109, 103601 (2012) arxiv.org/pdf/1111.1622.pdf I get there from livescience.com/… – tyoc213 Feb 19 '15 at 19:07

Not a full answer, but remember that any issue with path of particle must be done with a sum-over-paths (think it's called a Feynman integral) approach. I don't even think that $\angle i=\angle r$ is necessary for a single photon; it's only when we get multiple photons that interesting things happen.